This invention relates to methods, apparatuses and systems for isolating vibrations emanating from sources such as machinery, more particularly to those which implement at least one resilient element and which provide support for such sources.
It is environmentally desirable in many contexts to reduce transmission of vibrations to neighboring structure. For example, the U.S. Navy has an interest in attenuating the transmission, via connecting members to supporting structure, of unwanted vibrations from heavy machinery such as ship engines. Devices for reducing such transmission are generally known as vibration xe2x80x9cisolatorsxe2x80x9d because they serve to xe2x80x9cisolatexe2x80x9d the machine""s vibration from contiguous structure. A vibration isolator is used to join one object to another and to restrict, to some degree, the transmission of vibration. See, e.g, J. E. Ruzicka, xe2x80x9cFundamental Concepts of Vibration Control,xe2x80x9d Sound and Vibration, July 1971, pp 16-23, incorporated herein by reference. See also, Eugene (Eygeny) I. Rivin, xe2x80x9cPrinciples and Criteria of Vibration Isolation of Machinery,xe2x80x9d ASME Journal of Mechanical Design, Transactions of the ASME, Vol. 101, October 1979, pp 682-692, incorporated herein by reference. Both passive and active vibration isolation systems have been known in the art.
Passive vibration isolators have conventionally involved a passive damping arrangement which provides a resilient element (xe2x80x9cspringxe2x80x9d) along with a damping mechanism (xe2x80x9cenergy releaserxe2x80x9d), and which serves as a support (xe2x80x9cmountxe2x80x9d), for vibrating machinery or other structure. Passive vibration isolation devices, alternatively referred to as xe2x80x9cmountsxe2x80x9d or xe2x80x9cspringsxe2x80x9d or xe2x80x9cspring mountsxe2x80x9d in nomenclature, operate on the principle of low dynamic load transmissibility by a material having a resilient property. Passive mounts are designated xe2x80x9cpassivexe2x80x9d because their function is based upon their inherent property rather than on their ability to, in an xe2x80x9cactivexe2x80x9d manner, react to an in-situ condition.
Passive mounts have been known to use any of various materials for, the resilient element, such as rubber, plastic, metal and air. Elastomeric mounts rely primarily upon the resilience and the damping properties of rubber-like material for isolating vibrations. Mechanical spring mounts implement a helical or other metal spring configuration. Pneumatic, mounts utilize gas and an elastic material (such as reinforced rubber) as resilient elements in a bellows-like pneumatic spring assembly. A pneumatic mount or spring typically comprises a flexible member, which allows for motion, and a sealed pressure container or vessel having one or more compartments, which provides for filling and releasing a gas. Pneumatic springs are conventionally referred to as xe2x80x9cair springsxe2x80x9d because the gas is usually air. In conventional usage and as used herein the terms xe2x80x9cair spring,xe2x80x9d xe2x80x9cair mountxe2x80x9d and xe2x80x9cair spring mountxe2x80x9d are used interchangeably, and in the context of these terms the word xe2x80x9cairxe2x80x9d means xe2x80x9cgasxe2x80x9d or xe2x80x9cpneumatic,xe2x80x9d wherein xe2x80x9cgasxe2x80x9d or xe2x80x9cpneumaticxe2x80x9d refers to any gaseous substance.
Active vibration isolation has more recently become known in the art. Basically, a sensor measures the structure""s vibration, an actuator is coupled with the structure, and a feedback loop tends to reduce the unwanted motion. Typically, an output signal, proportional to a measurable motion (such as acceleration) of the structure, is produced by the sensor. Generally speaking, the actuator includes some type of reaction mass. A processor/controller processes the sensor-generated output signal so as to produce a control signal which drives the reaction mass, the actuator thereby producing a vibratory force, whereby the motion (e.g., acceleration) of the structure is reduced.
The three basic components of an active vibration isolation system are a motion sensor (e.g., a motion transducer), a processor/controller and a vibratory actuator. The sensor responds to vibratory motion by converting the vibratory motion into an electrical output signal that is functionally related to, e.g., proportional to, a parameter (e.g., displacement, velocity or acceleration) of the experienced motion. An accelerometer, for example, is a type of sensor wherein the output is a function of the acceleration input; the output is typically expressed in terms of voltage per unit of acceleration. The most common processor/controller is a xe2x80x9cproportional-integral-derivativexe2x80x9d-type (xe2x80x9cPIDxe2x80x9d-type) controller, a kind of servomechanism, which proportionally scales, and integrates or differentiates, the sensor response. The actuator is essentially a device adapted to transmitting a vibratory force to a structure; such an actuator has been variously known and manifested as an inertia actuator, inertial actuator, proof mass actuator, shaker, vibration exciter and vibration generator; as used herein, the terms xe2x80x9cactuator,xe2x80x9d xe2x80x9cinertia actuatorxe2x80x9d and xe2x80x9cvibratory actuatorxe2x80x9d are interchangeable and refer to any of these devices. The actuator generates a force, applied to the structure, based on the electrical output signal from the processor/controller.
Incorporated herein by reference are the following two patents: Jen-Houne Hannsen Su U.S. Pat. No. 5,899,443, issued 04 May 1999, entitled xe2x80x9cPassive-Active Vibration Isolationxe2x80x9d; and, Jen-Houne Hannsen Su U.S. Pat. No. 5,887,858, issued 30 Mar. 1999, entitled xe2x80x9cPassive-Active Mount.xe2x80x9d Also incorporated herein by reference is Jen-Houne Hannsen Su, xe2x80x9cRobust Passive-Active Mounts for Machinery and Equipment,xe2x80x9d Proceedings of DETC ""97, 1997 ASME Design Engineering Technical Conferences, Sep. 14-17, 1997, Sacramento, Calif. (nine pages).
In Su ""443 and Su ""858, Su discloses inventions which uniquely and efficaciously combine known passive vibration technology with known active vibration technology. According to either Su ""443 or Su ""858, one or more vibratory actuators are coupled with (e.g., attached to or mounted upon) the bottom attachment plate of a conventional mount. Su ""443 and Su ""858 further disclose placement of one or more motion sensors (for sensing, e.g., velocity or acceleration) at the bottom attachment plate so that the sensors and actuators are correlated in pairs, each sensor-actuator pair having one sensor and one actuator in a functionally and situationally propinquant relationship. The inventive mount disclosed in Su ""443 and Su ""858 is styled therein xe2x80x9cpassive-activexe2x80x9d because, proceeding generally downward from the above-mount object to the below-mount foundation, the object""s vibration is first reduced passively and then is further reduced actively.
Su ""443 and Su ""858 each teach the availing of active control so as to, in effect, increase the dynamic stiffness of the below-mount foundation. The impedance inherent in a realistic below-mount foundation falls short of the impedance inherent in an ideally rigid below-mount foundation. According to Su ""443 and Su ""858, the impedance differential between foundation reality and foundation ideality is largely compensated for by providing one or more inertia actuators on the bottom plate (e.g., retainer plate, mounting plate, backing plate, or end plate) of the mount, for example inside an air mount on its bottom plate.
Su ""443 and Su ""858 thus provide more effective, yet practical and affordable, vibration isolation methods, apparatuses and systems. Typically, the electronic components will be commercially available; the sensors, actuators and PID-type controllers appropriate for most inventive embodiments according to Su ""443 and Su ""858 will be xe2x80x9coff-the-shelfxe2x80x9d items which can be purchased at less than prohibitive costs. In accordance with Su ""443 and Su ""858, the sensors and actuators can be retrofitted in existing conventional mounts, or the inventive mount can be manufactured or assembled from scratch.
For many applications according to Su ""443 and Su ""858, the inventive mount will afford superior performance in isolating vibrations of an above-mount structure from a realistic below-mount foundation; for some applications, however, the inventive mount according to Su ""443 and Su ""858 can be used quite effectively for isolating vibrations of a below-mount foundation from an above-mount structure such as a piece of equipment. For applications involving heavy machinery, a multiplicity of inventive mounts can be utilized. For a single piece of heavy machinery, vibration isolation effectiveness can be expected to increase in accordance with an increase in the number of inventive mounts that are used.
The active vibration control aspect of the inventions disclosed by Su ""443 and Su ""858 serves to enhance the passive vibration control aspect of these inventions. The inventions of Su ""443 and Su ""858 are xe2x80x9cfail-safexe2x80x9d in a sense; in the event of inoperability of an inventive mount according to Su ""443 and Su ""858 (e.g., due to power failure or electromechanical failure), the performance of such inventive mount degrades to that of the conventional passive mount.
The inventions according to Su ""443 and Su ""858 typically obviate the need to fortify, for isolation purposes, the existing below-mount foundation. The foundation will be less expensive, since its design will involve only considerations concerning load-carrying capacity (e.g., static strength/structural integrity). Vibration-related considerations will not need to be addressed in foundation design; such factors as fatigue life, vibration and noise will be controlled automatically by the advanced mount according to Su ""443 and Su ""858.
Active control according to both Su ""443 and Su ""858 typically serves to complement the deficiency of the passive control in the low frequency. Conventional passive mounts are generally characterized by low frequency enhancement; conventional passive mounts typically have inherent low frequency resonance, and consequently may be ineffective or may even cause enhancement of dynamic load transmission at low frequency. In inventive practice according to Su ""443 and Su ""858, the low frequency disturbance enhancement due to the resonance frequency of the mounts should be more or less reduced, depending on the force output capacity of the actuators used for a given inventive embodiment.
Notwithstanding the significant advantages generally associated with practice of inventive vibration isolation according to Su ""443 and Su ""858, such practice according to Su ""443 and Su ""858 may be less than entirely satisfactory for certain applications. In particular, typical inventive embodiments according to Su ""443 and Su ""858 are suitable for a rather limited scope of isolation loading; that is, in effecting vibration isolation, a typical apparatus according to Su ""443 or Su ""858 is designed to be subjected to a relatively narrow range of weight, albeit the apparatus is highly effective for such purposes. Nevertheless, it is sometimes desirable to utilize vibration isolation apparatus which is applicable to a relatively broader scope of isolation loadingxe2x80x94that is, to a relatively wide range of weight to which the apparatus is to be subjected in effecting vibration isolation.
In view of the foregoing, it is an object of the present invention to provide method, apparatus and system for highly effective vibration isolation.
It is another object of this invention to provide method, apparatus and system for accomplishing same in association with a wide range of loads.
A further object of this invention is to provide such method, apparatus and system which are practical, relatively uncomplicated and cost-effective for many applications.
The present invention provides apparatus, system and method for vibration isolation, especially for reducing transmission of vibration of an object to a foundation for said object. Certain principles pertaining to the present invention""s passive-active elastomeric/viscoelastic isolator (mount) are the same as or similar to those pertaining to the passive-active air mount disclosed by Su ""443 and Su ""858. Notably and contradistinctively, however, the passive-active mount according to this invention is a xe2x80x9cconstant natural frequencyxe2x80x9d (abbreviated herein, xe2x80x9cCNFxe2x80x9d) passive-active mount. The CNF passive-active mount according to this invention affords wide load range application and simple implementation. The present invention""s passive vibration control is effectuated by one or more xe2x80x9cstreamlined resilient elements,xe2x80x9d each attributed with a xe2x80x9cconstant natural frequencyxe2x80x9d (CNF) quality whereby such element is naturally predisposed to passively reducing vibration at a particular frequency band regardless of the extent of the loading, within certain parameters, to which such element is being subjected. The CNF-endowed passive vibration control represents a significant improvement vis-a-vis"" Su ""443 and Su ""858.
Regis V. Schmitt and Matthew L. Kerr, xe2x80x9cA New Elastomeric Suspension Spring,xe2x80x9d Society of Automotive Engineers (SAE), Inc., SAE Paper No. 710058, Automotive Engineering Congress, Detroit, Mich., Jan. 11-15, 1971 (8 pages), incorporated herein by reference, disclose a constant natural frequency spherical elastomeric spring element. Schmitt et al. teach (Schmitt et al., first page) the advantageousness of xe2x80x9cmaintaining a constant natural frequency, on the primary suspension spring, with varying vehicle weight.xe2x80x9d A constant natural frequency is seen by Schmitt et al. as capable of xe2x80x9cproviding consistent ride quality with varying vehicle weight.xe2x80x9d As explained by Schmitt et al., xe2x80x9cNatural frequency is a function of spring rate and supported mass. Thus, it changes as supported mass changes if spring rate is a constant (linear spring). The contribution of a linear, or nearly linear, primary suspension spring to natural frequency changes with vehicle weight. This results in a compromise which gives best performance over only a part of the total range of truck weight expected.xe2x80x9d
Schmitt et al. (Schmitt et al., third page) tested a spherical elastomeric sample and found that it xe2x80x9cdoes, in fact, have a constant frequency characteristic.xe2x80x9d They further found xe2x80x9cthat, in the spherical spring, natural frequency is dependent on the size of the sphere and not on compound stiffness. Increasing compound stiffness (durometer) decreases the actual sphere deflection for a given load. The spring rate, hence natural frequency, for that load depends on the slope of the load deflection. curve at the point reached by that load. The shape of the load deflection curve and its slope for a given load is dependent on the size of the sphere and not on compound stiffness.xe2x80x9d In addition to a spherically shaped elastomeric sample, they tested elastomeric samples having xe2x80x9chourglassxe2x80x9d and xe2x80x9ctruncatedxe2x80x9d shapes.
Eugene (Evgeny) I. Rivin, xe2x80x9cPassive Engine Mountsxe2x80x94Some Directions for Further Development,xe2x80x9d SAE 1985 Transactions, Society of Automotive Engineers (SAE), Inc., SAE Paper No. 850481, Section 3, Vol. 94, 1986, pp. 3.582-3.591, incorporated herein by reference, discloses that xe2x80x9c[a] constant natural frequency (CNF) mount is characterized by a specific. nonlinear load-deflection characteristic when its vertical stiffness kZ is proportional to the applied weight load W, kZ=AW. Accordingly, vertical (bounce) natural frequency fZ is [constant]. To be a truly CNF mount, its spring rates in the x and y directions must also be proportional to W, or ratios kZ/kX and kZ/kY must be constant while the weight load varies in its rated rangexe2x80x9d
Rivin (1985) teaches that CNF xe2x80x9cmounts have several advantages, whose relative importance depends on the goals to be achieved. If decoupling is considered as an important goal, it can be much more reliably achieved by using CNF mounts . . . . Another unique advantage of the CNF mount is its insensitivity to rubber durometer variations . . . . If the rubber durometer deviates into lower values, . . . the natural frequency for a given weight load in the linear range becomes smaller. However, the natural frequency in the CNF range stays the same, although the range starts from a smaller weight load . . . . A similar effect occurs for a higher-than-nominal durometer . . . . In this case the natural frequency for a given weight load in the linear range becomes higher . . . , but the natural frequency in the CNF range is still the same.xe2x80x9dxe2x80x9cEugene (Evgeny) I. Rivin, xe2x80x9cVibration Isolation of Precision Equipment,xe2x80x9d Precision Engineering, 1995, vol. 17, pp 41-56, incorporated herein by reference, discloses (e.g., Rivin, 1995, p 55) the xe2x80x9cuse of constant-natural-frequency (CNF) isolators, in which stiffness in both vertical and horizontal directions is proportional to the weight load on the isolator. As a result, such isolators provide a high degree of dynamic decoupling without the need to determine the center-of-gravity position, to calculate weight load distribution between the mounting points, etc. In addition to this, such isolators have a significantly reduced sensitivity to manufacturing tolerances.xe2x80x9d
Eugene (Evgeny) I. Rivin, xe2x80x9cShaped Elastomeric Components for Vibration Control Devices,xe2x80x9d Sound and Vibration, July 1999, Vol. 33, no. 7, pp 18-23, incorporated herein by reference, teaches (Rivin, 1999, p 21) that xe2x80x9c[p]erformance of vibration isolators improves significantly if the isolator has a special nonlinear load-deflection characteristic whereas its stiffness is proportional to weight load on the isolator within a relatively broad load range (constant natural frequency or CNF characteristic).xe2x80x9d Rivin discloses spheres, radially loaded cylinders and radially loaded toruses as examples of xe2x80x9cshaped elastomeric components.xe2x80x9d It is taught by Rivin that the xe2x80x9cuse of shaped elastomeric components results in much more compact designs due to larger allowable compression deformations, under static loads. Larger compression deformations can be allowed due to a much more uniform stress distribution and lower maximum stresses/strains and lower creep rates as compared with conventional bonded rubber blocks made of the same rubber blend. In addition to these important advantages, it has been shown that the CNF isolators have a substantially lower sensitivity to production variations of rubber hardness than conventional isolators with linear load-deflection characteristics, resulting in much better performance uniformity. Thus, use of radially loaded rubber cylinders/toruses could significantly advance the state of the art for vibration isolators. Spherical rubber elements have the same, advantages (constant natural frequency in a relatively broad load range and reduced creep) and can be used for lightly loaded vibration isolators.xe2x80x9d
Evgeny I. Rivin U.S. Pat. No. 5,934,653, entitled xe2x80x9cNonlinear Flexible Connectors with Streamlined Resilient Elementsxe2x80x9d and issued 10 Aug. 1999, is hereby incorporated herein by reference. Rivin ""653 discloses a streamlined elastomeric (e.g., rubber) resilient element characterized by nonlinear load deflection. Disclosed by Rivin ""653 (e.g., Rivin ""653, col. 2) is xe2x80x9cthe use of streamlined rubber elements such as balls, ellipsoids, toruses, radially-loaded cylinders, etc.xe2x80x9d According to Rivin ""653, such streamlined resilient elements are characterized by significant (e.g., two to three times) increase in the allowable continuous compression deformation, and are further characterized by a progressively nonlinear deformation. Rivin ""653teaches the desirability of xe2x80x9cutilizing streamlined resilient elements without compromising their special deformation properties, which may be caused by their bonding to other elements.xe2x80x9d
The following U.S. patents, each of which is incorporated herein by reference, are also of note: Houghton, Jr. et al. U.S. Pat. No. 6,209,841 B1 issued 03 Apr. 2001; Krysinsky et al. U.S. Pat. No. 6,045,090 issued 04 Apr. 2000; Lee et al. U.S. Pat. No. 5,780,948 issued 14 Jul. 1998; Lee et al. U.S. Pat. No. 5,780,740 issued 14 Jul. 1998; Rivin U.S. Pat. No. 5,630,758 issued 20 May 1997; Cheng et al. U.S. Pat. No. 5,544,451 issued 13 Aug. 1996; Leyshon U.S. Pat. No. 5,016,862 issued 21 May 1991; Hall et al. U.S. Pat. No. 4,880,201 issued 14 Nov. 1989; Lafferty U.S. Pat. No. 4,619,467 issued 28 Oct. 1986; Shtarkman U.S. Pat. No. 4,509,730 issued 09 Apr. 1985; Stone et al. U.S. Pat. No. 4,452,329 issued 05 Jun. 1984; Barley U.S. Pat. No. 4,384,701 issued 24 May 1983; Madden U.S. Pat. No. 4,218,187 issued 19 Aug. 1980; Leingang U.S. Pat. No. 3,997,151 issued 14 Dec. 1976; Taylor U.S. Pat. No. 3,947,004 issued 30 Mar. 1976.
The present invention uniquely features the utilization of one or more shaped elastomeric (e.g., viscoelastic) elements (e.g., members) in order to increase the load range applicability of the xe2x80x9cpassivexe2x80x9d aspect of a passive-active mount such as disclosed by Su ""443 and Su ""858. These shaped or contoured elastomeric (e.g., viscoelastic) elements are referred to herein as xe2x80x9cstreamlined resilient elements.xe2x80x9d Typically, a CNF passive-active mount according to this invention will be uniquely characterized by a specific arrangement of one or more streamlined resilient elements along with one or more inertial actuators. The present invention""s CNF passive-active mount affords wide load range application and simple implementation.
Since the streamlined resilient element or elements maintain approximately the same mount resonance frequency for a wide range of isolation weight, the mount according to this invention is termed a xe2x80x9cconstant natural frequency passive-active mountxe2x80x9d (or, abbreviatedly, a xe2x80x9cCNF passive-active mountxe2x80x9d). At least one streamlined resilient element tends to impart a constant natural frequency (CNF) attribute to the inventive passive-active mount. Accordingly, the term xe2x80x9cstreamlined resilient element,xe2x80x9d as used herein, refers to any elastomeric (e.g., viscoelastic) object which has this kind of CNF-attributive quality when used in the context of vibration isolation. Because of its CNF-attributive quality, a streamlined resilient elementxe2x80x9d is also variously and synonymously referred to herein as a xe2x80x9cconstant natural frequency element,xe2x80x9d or a xe2x80x9cCNF element,xe2x80x9d or xe2x80x9ca streamlined CNF element,xe2x80x9d or a xe2x80x9cresilient CNF element,xe2x80x9d or a xe2x80x9cstreamlined resilient CNF element.xe2x80x9d
Generally, a xe2x80x9cstreamlined resilient elementxe2x80x9d will be characterized by a so-called xe2x80x9cstreamlinedxe2x80x9d shape, such as but not limited to that which describes one or more of the following: a spherical shape; a prolate spheroid (e.g., ellipsoid) shape adaptable to loading in either the short-axial or long-axial direction; a cross-sectionally circular segmented toroidal (doughnut) shape (e.g., a section of a cross-sectionally circular torus) adaptable to radial loading; a cross-sectionally noncircular (oval, e.g., elliptical) segmented toroidal (doughnut) shape (e.g., a section of a cross-sectionally oval torus) adaptable to radial loading, a cross-sectionally circular cylindrical shape adaptable to radial loading; a cross-sectionally noncircular (oval, e.g., elliptical) cylindrical shape adaptable to radial loading a cross-sectionally circular disk shape (which, actually, is an axially-longitudinally short form of a cylindrical shape) adaptable to radial loading; a cross-sectionally noncircular (oval, e.g., elliptical) disk shape (which, actually, is an axially-longitudinally short form of a cylindrical shape) adaptable to radial loading, a cross-sectionally circular toroidal (doughnut) shape adaptable to radial loading; a cross-sectionally noncircular (oval, e.g., elliptical) toroidal (doughnut) shape adaptable to radial loading; a toroidal shape, adaptable to radial loading, having a longitudinal (circumferential) axis of symmetry which defines a circular shape; a toroidal shape, adaptable to radial loading, having a longitudinal (circumferential) axis of symmetry which defines a noncircular (oval, e.g., elliptical) shape; a segmented toroidal shape, adaptable to radial loading, having a longitudinal axis of symmetry which defines a segment of a circular shape; a segmented toroidal shape, adaptable to radial loading, having a longitudinal axis of symmetry which defines a segment of a noncircular (oval, e.g., elliptical) shape; any truncated (e.g., flattened) version of any of the aforementioned shapes.
Generally, a streamlined resilient element will be at least substantially characterized by a curvilinear profile (such profile lying in an imaginary plane through the end plates and perpendicular thereto) which describes either a circular shape or a non circular shape such as an oval. According to frequent inventive practice, the streamlined resilient element is truncated at one or both ends, perhaps for the purpose of facilitating coupling of the streamlined resilient element with the end plates, and perhaps alternatively or additionally for the purpose of enhancing vibration isolation characteristics of the inventive mount. A streamlined resilient element which is truncated at either or both ends approximately or substantially defines the shape which would exist in the absence of such truncation.
According to typical embodiments of the present invention, there are two securement members connected, on opposite sides or ends, with the streamlined resilient element. The inventive CNF passive-active mount represents the xe2x80x9cisolatorxe2x80x9d entity. The mount includes two securement members, viz., an xe2x80x9cisolatee-entity-securementxe2x80x9d member and an xe2x80x9cisolated-entity-securementxe2x80x9d member. The mount""s xe2x80x9cisolatee-entity-securementxe2x80x9d member is the mount""s securement member which is attached to, or is attached with respect to, the xe2x80x9cisolateexe2x80x9d entity. The xe2x80x9cisolateexe2x80x9d entity is the, entity from which the xe2x80x9cisolatedxe2x80x9d entity""s vibrations are sought to be isolated. Another securement member of the mount, viz., the xe2x80x9cisolated-entity-securementxe2x80x9d member, is attached to, or is attached with respect to, the isolated entity. For most inventive embodiments, the isolated entity is an object (such as a machine) and the isolatee entity is a xe2x80x9cfoundationxe2x80x9d for the object. An important benefit of the present invention is its applicability to a wide range of masses (or weights) of the isolated entity.
Typically in accordance with this invention, each actuator has a companion sensor. Each sensor responds to a local vibratory motion of the mount""s isolatee-entity-securement member by sending a sensor feedback signal to a signal processor, which in turn sends a command signal to the sensor""s companion actuator, which in turn exerts or imparts a vibratory control force or motion upon the mount""s isolatee-entity-securement member. Each sensor continuously responds to the local vibration of the isolatee-entity-securement member, and the feedback loop inclusive of that sensor thus perpetuates. Each independent active vibration control subsystem includes a sensor and its corresponding actuator. The cumulative active vibration control system includes all of the individual active vibration control subsystems, each of which is uncomplicated.
When used herein adjectively to modify an inventive mount""s securement member, the words xe2x80x9cupper,xe2x80x9d xe2x80x9ctop,xe2x80x9d xe2x80x9clowerxe2x80x9d and xe2x80x9cbottomxe2x80x9d are terms of convenience which are intended to suggest structural and functional contradistinction rather than relative spatial positioning. Hence, in such contexts, the terms xe2x80x9cupperxe2x80x9d and xe2x80x9ctopxe2x80x9d refer to isolatee entity securement, i.e., securement of the mount with respect to the isolated entity, e.g., a vibrating object; the terms xe2x80x9clowerxe2x80x9d and xe2x80x9cbottomxe2x80x9d refer to isolated entity securement, i.e., securement of the mount with respect to the isolatee entity, e.g., a foundation for the vibrating object.
Typical inventive embodiments, in application, effectuate a xe2x80x9clocalizedxe2x80x9d vibration control approach rather than a xe2x80x9cglobalxe2x80x9d vibration control approach. Incorporated herein by reference is Su, Jen-Houne Hannsen Su et al., xe2x80x9cMechanisms of Localized Vibration Control in Complex Structures,xe2x80x9d Journal of Vibration and Acoustics, January 1996, Volume 118, pages 135-139. This paper is instructive regarding localized vibration control, which involves stabilization in localized areas of a structure, as distinguished from global vibration control, which involves stabilization of the entire structure.
Most active vibration control research, particularly in space structures applications, has dealt with controlling vibration in a global sense; the controller stabilizes the entire structure. When the interest lies in stabilizing only certain localized areas of the structure, the control objective can be focused and actuators/sensors are generally required only in the xe2x80x9ccontrol areas.xe2x80x9d This localized control approach can provide more effective vibration suppression in the control areas, and can require fewer actuators and sensors compared to global vibration control. Deciding where to mount sensors and actuators is somewhat simpler in a localized vibration control problem than in a general vibration control problem. For localized vibration control, sensors and actuators are usually located within the control areas, which usually represent together a relatively small portion of the entire structure.
A typical inventive vibration isolator according to this invention is adapted for engagement with a processor/controller (e.g., PID-type controller) which is capable of generating a control signal. The vibration isolator comprises a spring assembly, at least one sensor and at least one actuator. The spring assembly includes a top member (for securing the spring assembly with respect to an isolated entity), a bottom member and at least one interposed streamlined resilient element. The top member (typically a plate-type structure) is for securing the spring assembly with respect to an isolated entity. The bottom member (typically a plate-type structure) is for securing the spring assembly with respect to an isolatee entity (e.g., the foundation). Each streamlined resilient element is characterized by an approximately constant natural frequency (CNF) regardless of the loading imposed within a particular range of loading (e.g., weight).
Each streamlined resilient element is at least substantially composed of an elastomeric material and at least substantially has a contoured shape having CNF properties, such as spheroidal, prolate spheroidal, circular cylindrical, noncircular cylindrical, torroidal and torroidal segment. A disk is a kind of cylinder; the term xe2x80x9cdisk,xe2x80x9d as used herein, is a descriptive term for a cylinder characterized by a short axial length relative to its diameter. Each streamlined resilient element has the property of passively reducing vibration within a xe2x80x9cspecial passive-reduction-related frequency bandwidthxe2x80x9d which is at least substantially constant when the streamlined resilient element is subjected to a wide range in terms of the degree of loading. Cumulatively speaking, the one or more streamlined resilient elements are thereby capable, in net effect, of passively reducing vibration within a xe2x80x9cgeneral passive-reduction-related frequency bandwidthxe2x80x9d which is at least substantially constant when the one or more streamlined resilient elements are subjected to a wide range in terms of the degree of loading which is associated with the isolated entity and/or the isolatee entity. According to typical inventive embodiments, the xe2x80x9cgeneral passive-reduction-related bandwidthxe2x80x9d is approximately commensurate with the xe2x80x9cspecial passive-reduction-related bandwidth.xe2x80x9d
It is believed by the inventors that a streamlined resilient element has constant natural frequency attributes essentially because of the xe2x80x9cstreamlinedxe2x80x9d shape and the material resiliency (or elasticity) of the streamlined resilient element. In inventive operation, as higher load is applied with respect to the streamlined resilient element (i.e., the passive component), more material of the streamlined resilient element will come in contact with the attachment plates. Increased contact will render the streamlined resilient element stiffer, thereby maintaining the ratio of stiffness (spring rate) to load.
The one or more sensors, the one or more actuators and the processor-controller with which the inventive isolator is engaged represent components of a feedback loop system. Each sensor is coupled with the bottom member and is capable of generating a sensor signal which is in accordance with the vibration in a local zone of interest in the bottom member. Each actuator is coupled with the bottom member and is collocationally paired with one sensor so as to share approximate coincidence with respect to both physical situation and operational direction. Each actuator is capable of generating, in the local zone of interest of the sensor with which the actuator is collocationally paired, a vibratory force which is in accordance with the control signal which is generated by the processor/controller. The control signal is in accordance with the sensor signal which is generated by the sensor with which the actuator is collocationally paired. The vibratory force which is generated by an actuator has the tendency of actively reducing vibration within an xe2x80x9cactive-reduction-related frequency bandwidthxe2x80x9d which differs from the xe2x80x9cgeneral passive-reduction-related bandwidth.xe2x80x9d
Many embodiments of this invention implement a single sensor/actuator unit and a plurality of streamlined resilient members; typically, according to such embodiments, the collocated sensor/actuator unit is centrally located on the bottom plate, while the streamlined resilient members are peripherally located on the bottom plate. For such embodiments, the inventive feedback loop system will usually include a single feedback loop system. Other inventive embodiments implement a plurality of sensor/actuator units and at least one streamlined resilient member; typically, according to such embodiments, each streamlined resilient member will be centrally located on the bottom plate, while each of the plural sensor/actuator units will be peripherally located thereon, typically in symmetrical fashion about the center thereof. For such embodiments, the inventive feedback loop system will include a plurality of feedback loop subsystems. Generally, in inventive practice, the desired numbers, sizes, shapes and arrangements of the at least one streamlined resilient member and the at least one sensor/actuator unit will at least to some extent depend on the overall size and shape of the inventive constant natural frequency (CNF) mount and the force output capacity of the actuators selected.
An inventive configuration involving a single, centrally located sensor/actuator unit and plural, peripherally located streamlined resilient members may be preferable for many applications, due at least to greater compactness vis-a-vis"" other inventive configurations. For instance, an inventive configuration involving more than one centrally located sensor/actuator unit will generally take up more space than will an inventive configuration involving one centrally located sensor/actuator unit. Similarly, with regard to inventive embodiments wherein at least one streamlined resilient member is centrally located and at least two sensor/actuator units are peripherally located, an inventive configuration involving more than one centrally located streamlined resilient member will generally take up more space than will an inventive configuration involving one centrally located streamlined resilient member.
Regardless of whether one or more sensor/actuator units is inventively employed, each sensor is coupled with the bottom plate and generates a sensor output signal which is a function of the localized vibration of the bottom plate. The PID-type controller generates at least one control signal, each control signal being a function of its collocated sensor signal. Each actuator is coupled with the bottom plate above the bottom plate, wherein the sensors and actuators are in one-to-one correspondence; that is, each actuator is located proximate the corresponding sensor and generates a vibratory force which is a function of the control signal which is a function of the sensor signal generated by the corresponding sensor. Each feedback loop system or subsystem will include a sensor and an actuator, correlatively paired
For many inventive embodiments it is preferred that each sensor-actuator unit (sensor-to-actuator correlation) include xe2x80x9ccollocationxe2x80x9d of the sensor and the corresponding actuator; i.e., each collocated sensor-actuator pair is positioned in a kind of spatial and vectorial alignment, whereby the sensing of the sensor and the actuation of its corresponding actuator are approximately in the same direction. For some such inventive embodiments having at least two sensors and at least two actuators, all the collocational directions preferably are approximately parallel.
Some inventive embodiments manifesting collocational parallelism preferably manifest a kind of symmetry which may serve to optimize, perhaps even synergistically, the overall effectiveness of the individual localized active vibration control system or subsystems. For typical such embodiments, the centrally located entity or entities (whether this be at least one streamlined flexible member or at least one sensor/actuator unit) are characterized by a centric imaginary axis which is approximately vertical (i.e., approximately perpendicular to the bottom plate). This centric imaginary axis is approximately coincident with or approximately parallel to the approximately vertical (i.e., approximately perpendicular to the bottom plate) collocational direction of each sensor/actuator unit, as well as to the approximately vertical (i.e., approximately perpendicular to the bottom plate) imaginary axis of at least substantial symmetry of each streamlined flexible member. Every arrangement of the at least one sensor/actuator unit, in terms of their respective collocational directions, is characterized by approximate symmetry with respect to the centric axis. Similarly, every arrangement of the at least one streamlined flexible member, in terms of their respective axes of symmetry, is characterized by approximate symmetry with respect to the centric axis. Further, the top and bottom plates are typically congruous with each other so that their respective perimeters are also characterized by approximate symmetry with respect to the centric axis.
Typically, both the top (upper) and bottom (lower) members used for securing a conventional air mount are flat structures, e.g., plates. For illustrative purposes, the top and bottom plates are exemplified herein as each having a rectangular (in particular, a square) shape; nevertheless, in the light of this disclosure, it will be understood by the ordinarily skilled artisan that, in inventive practice, the top and bottom plates can each describe practically any shape, and that such shapes can differ from each other (e.g, they need not be comparable or similar). Generally in practicing the present invention, the lower plate""s upper surface will be available for inventive sensor-actuator implementation in combination with streamlined flexible member implementation.
The present invention features the utilization of one or more streamlined resilient elements. Any number, shape or combination of shapes of discrete (e.g., segmented) streamlined resilient elements is possible in accordance with the present invention. The CNF passive-active mount in accordance with the present invention can be used for a wide range of vibration isolation weight. The inventive mount is typically feasible for load ranges between as high as ten times to one hundred times the minimum load. In other words, generally speaking, the present invention""s CNF passive-active mount can operate in inventively appropriate CNF fashion in a load range which is extends between the minimum load and some large multiple thereof. According to some inventive embodiments, the load range is between the minimum load and ten times the minimum load. According to other inventive embodiments, the load range is between the minimum load and one hundred times the minimum load. According to most inventive embodiments, the load range will be between the a minimum load value and a multiple load value of the minimum load value, wherein the multiple load value is between ten times and one hundred times the minimum load value. That is to say, the wide (broad) range of loading, in terms of the degree of loading which at least substantially results from at least one of said isolated entity and said isolatee entity, is an approximate range which is between a minimum loading value and a maximum loading value; the maximum loading value is between about ten times and about one hundred times the minimum loading value.
Yet, the inventive mount typically is substantially smaller than the conventional mount designs which would seek to accomplish vibration isolation over broad loading ranges. Since each inventive CNF passive-active mount achieves vibration isolation over a broad loading range, a smaller inventory of inventive mounts will suffice for many purposes. Moreover, the typical inventive mount is characterized by lower heat, generation than characterized conventional mounts. Many inventive embodiments are configured so as to provide good heat ventilation for the active component (e.g., the component which includes at least one collocated actuator/sensor pair). The same or similar inventive CNF passive-active mount design can be used at different locations or on different types of foundations. The present invention has a simple non-pneumatic design which advantageously admits of easy fabrication. Furthermore, the typical inventive mount has snubbing/captive capability for shock control.
Other objects, advantages and features of this invention will become apparent from the following detailed description of the inventions when considered in conjunction with the accompanying drawings.